(1) Field of the Invention
The present invention generally relates to a ball grid array package (BGA), and particularly to an arrangement of ground connection in a ball grid array package.
(2) Description of the Prior Art
A ball grid array package (BGA) is a technology used for packing a semiconductor chip. The packing efficiency of the ball grid array package is very high. Therefore, with the trend of electronic components and devices becoming smaller and smaller, the ball grid array package with high packing efficiency and yield rate is used generally.
Please refer to FIG. 1. A typical ball grid array package 10 is illustrated in FIG. 1. The package 10 usually includes a semiconductor ship 11. The chip 11 is disposed on a top surface of a substrate 12 and is electrically connected to the substrate 12. Also, the chip 11 is usually adhered on the top surface (chip adhering surface) of the substrate 12 by an adhesive.
As shown in FIG. 1, several electrically conductive wires 13 are used for electrically connecting the chip 11 and the substrate 12. An encapsulating material 15 covers the chip 11 and a portion of the substrate 12, for avoiding the chip 11 and the portion of the substrate 12 from moisture and pollution. The substrate 12 is usually a multi-layer structure. For example, the substrate 12 can have two signal layers, one ground layer and one power layer. The ground layer and the power layer are disposed between the two signal layers.
Several solder balls 14 are disposed on a bottom surface of the substrate 12, so that an outer circuit or another electronic apparatus is able to easily electrically connect to the chip 11 through the package 10. The solder balls 14 can be sorted as source balls, signal balls or ground balls according to the circuit that the solder balls 13 are electrically connected to. The source balls are used for supplying power. The signal balls are used for transmitting signals. And the ground balls are used for proving a reference electric potential.
Along with the trend of the electronic components and devices becoming smaller and smaller, the operation speed thereof is promoted as well. Also, the circuit integration of the electronic components and devices increases. In the condition of high operation speed, signals are not transmitted according to preset circuits more frequently. As a result, noise occurs and even the chip sometimes does not function normally. Therefore, in the condition of high operation speed, it is very important to control the impedance between the signals, reduce the electromagnetic interference (EMI), decrease the interference between the signals and suppress coupling effect of noise.
Generally speaking, the transmission of the signal is completed when the an induced return current is transmitted to the nearest ground terminal. In a prior art, several (usually more than eight) signal balls refer to a ground ball in common. As a result, the signal transmitted to the ground ball sometimes needs to wait or find the reference electric potential of another ground ball. When the operation speed is promoted or when the circuit integration is increased, noise occurs more frequently. Also, the chip does not function normally more frequently.